31 Weeks

Heidi McDowell/istock

Nov 17, 2009

You know the sensation where you feel like you're falling even though you're lying securely in bed? Babies feel this in utero when a mom's sudden movement causes them to fling out their arms and legs reflexively (called the Moro reflex). This startle reflex starts in the third trimester and continues after birth (see our tips for a swaddling technique that will help ease that flailing feeling), and some parents may confuse the reflex with seizures because it's often accompanied by trembling.